The rapidly evolving technology of gene transfer offers novel and potentially important strategies for the prevention and treatment of human diseases. The current proposal applies viral mediated gene transfer with the intention of altering the beta-cell destructive autoimmune response characteristic of NOD mice. Three general approaches are proposed each targeting the response at a unique site in the diabetogenic immune pathway. In Aim 1, we will target the terminal phase of the response that is observed in the vigorous destruction of islet grafts transplanted to NOD mice that have already developed diabetes. We will determine whether autoimmune destruction of transplanted islets can be prevented by direct gene transfer to islet grafts using Adenoviral vectors carrying genes encoding either immune suppressive or tolerogenic molecules. To accomplish this, we will take advantage our extensive experience with Adenovirus mediated gene transfer to pancreatic islets and a large panel of Adenoviral constructs readily available to us. In Aim II, we will attempt disease prophylaxis in the pre-diabetic period by Adenoviral mediated gene transfer directly to the pancreas of mice expected to become diabetic. We hypothesize that the local expression of immunosuppressive or tolerogenic molecules may abort or reverse beta cell destruction even after initiation. Thus pre-diabetic mice will be treated at time points either before or after the expected development of insulitis and immediately after demonstrating overt diabetes. In Aim III, we will conduct studies designed to prevent the disease process prior to its initiation through modification of the T cell repertoire during its thymic ontogeny. We have recently developed a model of direct gene transfer to the thymus that is ideally suited for these experiments. This will allow us to determine whether the thymic expression of either immunoregulatory molecules such as MHC class II, or the leading candidate for a diabetogenic autoantigen, GAD65, will eliminate or down regulate the clones of T cells responsible for autoimmune beta-cell destruction. We expect these studies will not only lead to the development of relevant therapeutic strategies, but also will further our understanding of the sequence of immunological derangements that result in autoimmune beta-cell destruction.